Executive Summary:NCRP Report No. 155, Management of Radionuclide Therapy Patients, is intended for use by a wide readership including physicians, medical physicists, health physicists, administrators, nurses, other professional and medical staff, and patients. The approaches originally suggested in NCRP Report No. 37, Precautions in the Management of Patients Who Have Received Therapeutic Amounts of Radionuclides (1970), are incorporated and updated. This Report makes recommendations on explaining risks from therapeutic procedures and obtaining adequate, informed patient consent; dose limits for members of the patient's family; patient confinement in a hospital or skilled-care facility; and patient records including the radionuclide and activity used, the treating physician, and contact information. Section 1 of Report No. 155 is an introduction and includes some brief historical items. This Section discusses the basic principles of both radiopharmaceutical therapy and brachytherapy. Section 2 deals with basic radiation safety principles in a medical facility and includes a description of the radiation safety program, dose limits, staffing and definitions specific to this Report. Section 3 addresses radiopharmaceutical therapy including both clinical and radiation safety aspects. Appendices A and B expand on the patient release criteria outlined in Section 3 and include a spreadsheet program for assisting in determining patient release instructions. Section 4 deals specifically with brachytherapy including techniques, terminology, and a brief discussion of applicable dosimetry. Section 5 includes facility design for both nuclear-medicine and radiation-oncology installations. Section 6 describes changes in patients' status, including medical emergencies and includes guidelines for other situations that may be adapted to readers' facilities. Appendix C presents a discussion of quality-assurance requirements for high dose rate afterloading which is an increasingly useful modality. Appendix D outlines shielding requirements for high dose rate brachytherapy installations.